Miniature photocells and method of making the same



Dec. 18, 1962 F. P. sTRoTHER 3,069,487

MINIATURE PEoTooELLs AND METHOD oF MAKING THE `SAME Filed Jan. 4, 1960 2 Sheets-Sheei'I l FGJ. F102.

WMM, fr M ATTORNEYS Dec. 18,

Filed Jan.

F. P. STROTHER MINIATURE PHOTOCELLS AND METHOD OF MAKING THE SAME 2 Sheets-Sheet 2 FIG. Z

INVENTOR FRED P STROTHER- BYJMW,

ATTORNEYS United States Patent C) M MINIATURE PHOTOCELLS AND METHOD F MAKING THE SAME Fred P. Strother, Shawmut, Ala., assigner to West Point Manufacturing Company, West Point, Ga., a corporation of Georgia Filed Jan. 4, 1960, Ser. No. 405 3 Claims. (Cl. 13d-S9) This invention relates to photocells, and in particular to miniature photocells adapted to be positioned in locations of diiicult access. The invention relates also to -groups of miniature photocells arrayed in close order, and to methods of making the photocells.

A principal object of the invention is the provision of multiple photocells of miniature size, adapted for use in automation, data reduction, process control and the like where operation or control by means of a number of closely spaced and individual photocells is desired. Another object of the invention is to provide a compact photocell unit comprising large numbers of closely spaced and individual photocells, which may be arranged in line or in two-dimensional arrangement. In accordance with the present invention, for example, it is possible to provide a photocell array comprising more than 250,000 individual photocells per square inch.

A further object of the invention is the provision of a miniature photocell which may be operatively positioned in ordinarily inaccessible places, for example within the human body, which photocell is both rigid and self-supporting. Other objects of the invention are the provision of novel miniature photocells and miniature photocell arrays wherein electrical connection to each individual photocell may -be readily made in simple, quick fashion. The photocells, further, lend themselves to simplified and inexpensive manufacture, by mass production methods.

Other objects of the invention are to provide novel methods of manufacturing miniature photocells and miniature photocell arrays, by simple and economical procedures. Further objects of 4the invention will be in part evident, and in part pointed out hereinafter.

The invention and the novel features thereof may best be made clear from the following description and the accompanying drawings, in which FIGURE 1 is an elevational sectional view of an exemplary embodiment of the present invention, on enlarged and exaggerated scale, taken on the line 1-1 of FIG- URE 2;

FIGURE 2 is a transverse sectional view taken on the line 2 2 of FIGURE 1;

FIGURE 3 is a diagrammatic view illustrating a simplified method for initially arranging a plurality of wires for incorporation into a rigid matrix;

.JFIGURE 4 is an elevational sectional view of another embodiment of the invention, taken on the line y4,-4 of FIGURE 5;

FIGURE 5 is a transverse sectional view taken on the 1ine,5-5 of FIGURE 4; FIGURES 6-9 are a series of views illustrating one mode .of manufacture of a modified photocell in accordance with the invention. FIGURE 6 is an elevational sectional wiew of a single wire embedded in a metal tube, the assembly being faced oit ilush in a plane perpendicular to the wire axis;

FIGURE 7 is a view of the assembly of LFIGURE 6, after the .metal tube end has been extended lbeyond the enclosed wire and insulation by coating;

. VFIGURE 8 is a view of the assembly of "FIGURE 7 vafter the face end thereof has been coated with photosensitive material;

FIGURE 9 illustrates the condition of the FIGURE 8 3,069,487 Patented Dec. 1S, 1962 assembly, after removal of all photosensitive material except from the recessed insulated wire end;

FIGURE 10 is an elevational sectional view of a photocell array comprising units of the type illustrated in FIG- URE 9, taken on the line 10-10 of FIGURE 1l, and

FIGURE 1l is a face end View of the photocell array of FIGURE 10.

In the drawings, FIGURES l and 2 illustrate a simple embodiment of the present invention, wherein a plurality of insulated wires 20, each bearing an insulating coating 22 thereon, are arranged in closely spaced parallelism and embedded in a conductive matrix 2,4. The wires may be commercial copper wire of small diameter, `for example .001 inch diameter, and spaced apart from each other about .001 inch, `whereby 500 wires may be arranged to the lineal inch, or 250,000 to the square inch. It will be understood that wires of smaller diameter may be ernployed with less spacing therebetween, whereby arrays with 1,000 or more to the inch may be constructed. The conductive matrix 24 may be composed of low melting metal alloy, or may be resin filled with a large proportion of conductive particles, such as metal or carbon. Common aldehyde resins highly filled with metal or carbon particles are entirely suitable.

In the embodiment illustrated, corresponding ends 26 of the wires 20 terminate ilush with the surface 28 of the matrix, the surface 28 being preferably normal to the wire axes. As will be understood, the surface 28 may be planar, curved or otherwise.

As illustrated in FIGURE l, the matrix surface 2S .and wire ends 26 are coated with a layer 30 of photosensitive material. The free wire ends 32 may be of any desired length, and are adapted to be separated from their fellows `and individually connected to different circuits. The conductive matrix 24 serves `as a common termin-al, :and electrical connection thereto may be made in any conventional fashion, as by soldering wire thereto. As will be understood, each free wire end 32 constitutes the other terminal `of lan individual photocell, and may be connected to its own circuit. Each individual photocell is in essence .a ring of photosensitive material extending `between a wire end and the surrounding matrix, over the insulating coating 22 of the Wire. As the photosensitive material layer 30 has nite thickness, there is a certain amount of rdispersion of electrons therein as well as `of the light entering the material, whereby the described assembly approximates a point form if the overall diameter is quite small; that is, the cell functions in the manner of a disc, rather than as 1a ring.

The ywires 20 may be 'arranged in closely spaced parallelism, and then maintained or xed in such relationship by application of the conductive matrix to the assembly. One simple procedure is arranging the wires as illustrated in FIGURE 3, where-in is utilized a relatively large diameter `cylinder y34 provided with ya longitudinal recess 36, in Ithe shape of a keyway, extending along a side thereof. As illustrated, a continuous wire y38 may be wound about the cylinder 34 with desired spacing between adjacent convolutions. In using insulated Wire, no spacing is required, `and the convolutions may be wound side by side. If greater spacing is desired, it may be readily effected by appropriate grooving or threading on the cylinder 34, lor -two wires 38 may be wound simultaneously side by side, Ianti one subsequently removed to leave the other in desired spaced relationship.

After the desired number of convolutions are wound, the wire layer may be embedded in the Vmatrix by applying the matrix to the wire laye-r in and above the recess 36. As will be evident, the Wire sections extending across the recess are necessarily straight and panallel. The matrix may be lappropriately set or hardened after application, lwhereupon the wire layer may be cut above either edge of the recess 36, the wire layer thereby yielding a very large number of closely spaced wires embedded at one end in the matrix. The diameter of the cylinder 34 will determine the length of the free wire ends. The sub-assembly m-ay then be ground or buffed on its end surface corresponding to the cut line previously referred to, whereby -the wire ends 26 and matrix surface 23 are made ilush, and lie in a common plane, as illustrated in FIGURE l.

The photosensitive layer 3d is next applied to the surface composed `of the matrix and the wire ends 26. Any material having photosensitive characteristics may be employed, including photo-resistive, photo-voltaic and photoemissive material-s. Suitable materials, for example, include cadmium sulphide, cadminum selenide and antimony trisulphide. The coating may be applied in any manner adapted to effect a uniform thin material layer, including by evaponation, settling, spraying and the like. For the purposes of the present invention, it is preferred that the photo-sensitive layer 3l) be so thin as to be light permeable. That is, in use some light must completely penetnate the layer 3l) in order -to provide requisite electron excitation. The term light is used as inclusive of radiation of any wave length covering the entire range from ultra-violet to infra-red.

The preferred method `of applying the photo-sensitive material layer `3G is 4by sputtering or evaporation in -a vacuum. In the case of cadmium selenide, for example, a layer thickness of the order of .0001 inch is useful, and the application may be controlled by evaporating a predetermined quantity `of material under established conditions, or by utilizing a glass plate as a visual control, the proper thickness of coating being detected by color change of the control plate.

If the photosensitive material is applied otherwise than by evaporation, it may be necessary to consolidate or sinter the photosensitive material laye-r, and this is accomplished advantageously by heating the coated assembly after application of the coating material to appropriate temperature. T he photosensitive layer may then be sensitized by any conventional and :appropriate method, eg. by treatment with halogens and copper salts.

In the ease of some photosensitive materials, it is advantageous to subject the material after application to ionic bombardment in a vacuum, to improve or modify the final :characteristics of the photocells. Typically, such bombardment may be carried out for a period of from about 30 seconds to about 2 minutes under a pressure .of the order of l mm. yof mercury. In the present case, if the photosensitive material is applied by evaporation, the bombardment may be conveniently effected before removal from the vacuum chamber.

In :some applications, it is desirable that the face contact between the photosensitive material and the wires be ohmic or non-rectifying in character. This can be edectively accomplished by providing an extremely thin flash coating of indium .or gallium therebetween, conveniently in the vacuum coating step.

Application and sensitization of the photosensitive material layer completes the manufacture of the photocell array. As previously indicated, the conductive matrix 24 serves as a common terminal, and connection to each individual photocell may be made through the individual free wire ends 32, the photosensitive material lying 1mmediately over each wire end 26, including its insulation, functioning as an individual photocell. While in the example the photosensitive layer 30 is continuous, the relative resistance between one cell and adjoining cells is so great that the array functions substantially .as if the photosensitive layer were discontinuous between cells.

In the above description of the winding operanon, winding a single wire layer will effect a photocell array in in-line arrangement. Two dimensional arrangements may be produced in. similar fashion. For example, 1n

winding insulated wire without spacing, a plurality of wire layers may be wound, one on another. If the winding is with spacing, similar spacing between successive layers may be achieved by interposing thin sheets of matrix material. In this manner, a uniformly spaced arrangement may be effected as illustrated in FIGURE 2.

In accordance with another embodiment of the invention, each wire 2t) may be embedded inside a metal tube, by means of a cement or similar material. Stainless steel tubing, for example, is commercially available in sizes as small as .005 inch in outer diameter, whereby they may be arranged 200 to the inch in line and in twodimensional array. FIGURES 4 and 5 illustrate a miniature photocell array wherein each uninsulated wire 40 iS cemented in a metal tube 42. by means of a cement 44. Necessarily, if uninsulated wires are used, the cement 44 should be an electrically insulating cement, such as ceramic cement, epoxy resin or the like. If the wires are insulated, any suitable cement may be employed. Each wire may be readily and effectively centered and cemented in its associated tube by initially passing the wire through the tube, applying a drop of Cement material t0 the protruding wire end, and then drawing the wire end back into the tube. The cement material, if of proper consistency, will completely surround the wire within the tube, and on appropriate hardening of the cement material, the wire will be securely mounted in and electrically insulated from the tube. Another procedure is to apply a drop of the cement material to the wire end 0r to the tube end, and then insert the wire into the tube.

The metal tubes, each with a wire mounted therewithin, may then be positioned side by side in desired arrangement, with their corresponding ends substantially aligned and embedded in a conductive matrix material adapted to maintain the array in desired relationship. Since the tubes are metal, common solder is a particularly convenient matrix material. After the matrix has hardened, the surface 46 of the assembly may be ground or otherwise leveled off, whereby the tube ends and wire ends are made flush, whereupon the photosensitive material layer 30 may be applied thereto as previously described. As in the embodiment of FIGURES 1 and 2, the matrix serves as a common terminal and each free wire end 32 as the other terminal of an individual photocell.

As will be evident, the miniature photocells of the array of FIGURES 4 and 5 may be manufactured and utilized as individual photocells. This involves merely embedding a single wire in a tube as described, grinding an end flush, and applying photosensitive material to the flush end. The photocell is rigid `and self-supporting, and may be readily disposed or mounted in many locations of diicult access, by means of the metal tube. Electrical connection to the miniature photocell offers no diiiiculty, the tube serving as one terminal and the free end of the wire serving as the other.

The photocells illustrated in FIGURES 4 and 5, individually or in arrays, may be modified in accordance with the procedure described in connection with FIGURES 6-9, this representing a somewhat more sensitive and efficient construction. FIGURE 6 illustrates an individual photocell comprising an uninsulated wire 40 embedded in a metal tube 42 by means of an insulating cement 44, the outer surface 46 being ground flush. The assembly is then treated to recess the wire 40 and insulation 44 slightly within the metal tube 42, to form a shallow pocket 48 above the end of the insulated wire, as illustrated in FIGURE 7. This may be accomplished by mechanically removing the exposed end of the wire and insulation to the required depth, or more conveniently by extending the metal tube by coating additional metal thereonto. The coating of additional metal onto the exposed end of the metal tube may be accomplished most readily by selective electrodeposition of metal onto the end of the metal tube, to the exclusion of the insulated wire end, either in solution or in a vacuum. Deposition of metal onto the insulation wire end may be prevented by masking, or more conveniently by maintaining the metal tube at a potential different from that of the wire and insulation.

The photosensitive layer 30 may then be applied as previously described, the resultant coating, as illustrated in FIGURE 8, filling the pocket 48 and overlying the tube end. As will be recognized, the depth of the pocket 48 may be predetermined to correspond to the desired thickness of photosensitive material, and the applied layer of photosensitive material may then be buffed or similarly mechanically finished down to the tube end, leaving, as illustrated in FIGURE 9, a thin disc S0 of photosensitive material in the pocket 48. The photosensitive material disc 50 may thereafter be sensitized and processed as previously described. As will be understood, this construction is advantageous in that the tube Wall enclosing the pocket 48 functions as a lateral light barrier for the enclosed disc 50.

Photocells of the type illustrated in FIGURES 6-9 may, of course, be constructed in the form of a photocell array, as illustrated in FIGURES 10 and 1l. This may be done, in accordance with one exemplary procedure, by arranging a plurality of the metal tubes, each with a wire mounted therewithin, in substantial alignment, and embedding the tubes in a conductive matrix such as solder. The assembly may be finished flush, and recessing of the insulated Wire ends accomplished as by coating metal onto the exposed matrix surface, including primarily the metal tube ends. The photosensitive layer may then be applied and removed at the level of the tube ends, leaving a thin disc 50 of photosensitive material in each pocket 48 overlying an insulated Wire end. The photosensitive material discs 50 may thereafter be sensitized and processed as previously described, in a single operation. FIGURES 10 and 11 illustrate a closely packed array, wherein adjacent metal tubes 42 are substantially in contact. As previously described, the tube walls enclosing the pockets 48 function as light barriers with respect to the photosensitive discs 50, contributing materially to improved sensitivity and efficiency.

It will thus be seen that there has been provided by this invention an article and method in which the various objects hereinbefore set forth, together with many practical advantages, are successfully achieved. As various possible embodiments may be made of the novel features of the above invention, all without departing from the scope thereof, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.

I claim:

1. A miniature photocell array comprising a plurality of closely spaced insulated wires, said wires being ernbedded in and maintained in arrayed relationship by an in situ formed rigid matrix of conductive material, cor-I responding ends of said insulated wires and said matrix terminating substantially in a common surface, and a thin light permeable layer of photosensitive material on the corresponding end faces of said insulated wires, said matrix constituting a common terminal and the other end of each wire the other terminal of an individual photocell.

2. A photocell array as defined in claim 1, wherein the matrix is flush with the corresponding ends of said insulated wires, and said photosensitive material layer is continuous.

3. A photocell array as defined in claim 1, wherein the matrix extends slightly beyond the corresponding ends of said insulated wires, and said photosensitive material is confined to the pockets so defined above the insulated wire ends.

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